The invention relates to a polyphonic numerical synthesizer of periodic signals for use in generating musical sounds and in particular to electronic musical instruments provided with such synthesizer circuitry.
The present invention is an improvement over known synthesizer circuitry in which each analog sample value fed to an output channel is derived from a plurality of numerical data commensurate with the instantaneous phase, the octave and the amplitude of the sound to be produced. Information corresponding to this indispensable data is stored in a plurality of random memories. The memories may be programmed by means of a control circuit, preferably using a microprocessor which is operable independantly of the synthesizer circuitry. Such prior art synthesizer circuits are described in my patents 4,344,343, 4,149,440, 4,217,802 and 4,279,186.
The disclosure of said patents is included herewith by reference.
In the known synthesizer circuits the number of basic frequencies is limited. The term "basic frequency" is intended to designate a frequency from which further frequencies may be derived, generally by successive division (octaves). All frequencies of the synthesizer circuit, and this is common practice, are derived from oscillators (at least 12 in chromatic tuning), the number of said oscillators, however, being limited. Alternatively, the plural oscillators may be replaced by one single oscillator plus divider circuits which receive the output of the oscillator. In either case, however, in order to generate certain complex sounds, it becomes necessary to employ frequencies not contained in the number of available frequencies from the oscillators or dividers. The addition of further oscillators or further divider circuits in order to permit the generation of these complex sounds would render a synthesizer circuit very complex, and consequently the manufacture thereof would be quite expensive.